The objective is to investigate the effect of walnuts on gut microbiota, inflammatory markers, atopic dermatitis status, and indices of allergy outcomes in breastfed infants during early complementary feeding.

The three primary aims include:

Aim 1: Evaluate the effect of walnut consumption on gut microbiota structure and function, inflammation, atopic dermatitis, and allergy outcomes.

Aim 2: Evaluate the impact of walnut consumption on infant growth trajectories and risk of overweight.

Aim 3 (exploratory): Identify walnut-specific food signatures that are associated with gut microbiota and immunity biomarkers using a novel nutri-metabolomics technique.

Some details are intentionally left to out to preserve the scientific integrity of the study, and they will be included in the record after the study is completed.

Inclusion Criteria:

• Full term: gestational age ≥ 37 weeks
• Generally healthy without conditions that would affect normal growth
• No significant consumption of complementary food (e.g., no more than 1 oz of solid foods per week)
• Exclusively breastfed (< 2 weeks of cumulative formula exposure)

Exclusion Criteria:

• Adults unable to consent
• Pregnant women
• Prisoners